In impact printers, such as the Model No. 7221 impact printer manufactured by the present assignee of this invention, the printer can produce an objectionable level of noise. The printer generates a 1,200 Hz sound wave that, at elevated decibel levels, becomes annoying to the human ear. The sound wave is due in part to the wires of the impact print head, which slap at the paper in a small, concentrated, bubbled area. This bubbled area comprises a small air space that inherently forms between the receipt paper and the platen in receipt printing apparatus of this type.
It has been discovered by the present inventor that the noise generated in this bubble area can be greatly reduced by redesigning the ribbon cassette. This inventor has found that by keeping pressure on the receipt paper as it feeds over the platen, the bubble is substantially reduced or eliminated. This in turn reduces the noise during operation.
Two prongs have been added to the front of the cassette, about the ribbon window. These prongs straddle the striking area of the print head, and provide biasing against the paper bubble. The prongs act as spring retainers or pressure bumps that apply pressure to the paper as it passes before the impacting wires of the print head.